1. Field of the Invention
The present invention relates to encapsulation compositions in which an encapsulate is encapsulated in a glassy matrix. More particularly, the present invention relates to flavor encapsulation compositions in which a flavoring agent is encapsulated in a glassy matrix. The present invention further relates to processes for preparing such compositions.
2. Discussion of the Background
The encapsulation of encapsulates is an area of active research. In particular, the encapsulation of encapsulates such as medications, pesticides (including insecticides, nematocides, herbicides, fungicides, microbiocides, etc.) preservatives, vitamins and flavoring agents is desired for a number of reasons. In the case of medications and pesticides, encapsulation may be desired to achieve the controlled release of the medication or pesticide. For vitamins, encapsulation may be carried out to protect the vitamin from air-oxidation and, thus, to extend shelf life of the vitamin. In the case of flavoring agents, the encapsulation may be carried out to place the flavoring in an easily metered form which will release the agent at a controllable event, such as the addition of water.
It is generally known to skilled practitioners in the field of flavor encapsulation that the current practical commercial processes leading to stable, dry flavors are limited in great part to spray drying and extrusion fixation. The former process requires emulsification or solubilization of the flavor in an aqueous carrier containing the encapsulation solids, followed by rapid drying in a high temperature, high velocity gas stream and collection as a low-density bulk solid.
While spray drying accounts for the majority of commercially encapsulated flavor materials, several limitations of the process are evident. Low molecular weight components of complex or natural flavor mixtures generally exhibit high vapor pressures and are usually lost or disproportionate during the process. The resultant flavor-carriers are porous and difficult to handle. In addition, deleterious chemical reactions such as oxidation can result on surfaces exposed during and after drying. The final product, a dry, free flowing powder, will release the encapsulant rapidly upon hydration whether rapid release is desired or not.
U.S. Pat. No. 3,971,852 discloses the use modified starch, gums and other food polymers with low molecular weight polyhydroxy compounds and spray drying to yield a glassy matrix with encapsulated oil at a maximum of 70-80% by volume. The system forms a shell surrounding the oil flavoring but is limited to lipophilic flavoring agents.
U.S. Pat. No. 4,532,145 discloses a process for preparing compositions in which a volatile flavorant is fixed by spray drying from a carrier solution made up of 10-30% of a low molecular weight component such as a sugar or edible food acid with the balance of the solids being a maltodextrin carbohydrate in the amount of 70-90%.
U.S. Pat. No. 5,124,162 discloses a carrier mixture composed of mono- and disaccharides (22-45%), maltodextrins (25-50%), and a high molecular weight carbohydrate such as chemically modified starch, gum arabic or gum acacia (10-35%) to which flavoring agents are added and the subsequent solution is spray dried to yield a free flowing powder with a bulk density of 0.50 g/cc.
U.S. Pat. No. 5,601,760 discloses a carrier mixture utilizing whey protein isolates to encapsulate lipid flavor systems. The protein constitutes 35 to 100% of the encapsulating matrix with the remainder consisting of sugars. Other disclosed proteins include whey protein concentrates, β-lactoglobulin and α-lactoalbumin.
However, a number of technical issues are unmet by these approaches. First, thermally sensitive flavors undergo undesirable reactions including oxidations, rearrangements, and hydrolyses. Secondly, volatile components are lost or disproportionate during atomization and evaporation in the dryer.
A second process route, melt encapsulation, has been utilized to advantage with lipid-based flavors. In this technology, a melt is prepared by boiling off sufficient water from a high solids carbohydrate syrup, adding flavoring oils with an emulsifier, agitating under pressure to emulsify the oil in the melt and injecting the mixture into a chilling, dehydrating solvent bath to obtain fine rod-like filaments. After solvent removal, the matrix is reduced in size and, in some cases, coated with an anti-caking agent before being packed. See, e.g., U.S. Pat. Nos. 2,809,895; 3,041,018; 2,856,291; 2,857,821; and 3,704,137. Subsequent improvements in the art are disclosed in U.S. Pat. No. 3,314,803, for the encapsulation of volatiles such as acetaldehyde, and in U.S. Pat. No. 4,707,367, which discloses encapsulation of up to 35% by weight flavor oil in the glassy matrix.
U.S. Pat. No. 4,689,235 discloses the use of modified starch-maltodextrin carriers in the range of 5 parts modified starch:95 parts maltodextrin to 95 parts modified starch:5 parts maltodextrin. The carrier is dissolved to form a syrup, the water is cooked off, flavor is added and emulsified, and the melt is injected into a solvent bath.
An alternative route to encapsulating flavors is disclosed in U.S. Pat. No. 4,230,687. In this approach, high molecular weight carriers such as proteins, starches and gums are plasticized by addition of significant amounts of water in the presence of the encapsulate and subjected to a high shear dispersing process. The rubbery or plastic matrix with encapsulate is then extruded, recovered and dried to yield a stable product.
Another alternative process, melt extrusion, can be utilized for flavor fixation and encapsulation. In this process, a melting system, i.e., an extruder, is employed to form the carrier melt in a continuous process. The encapsulated flavor is either admixed or injected into the molten carbohydrate carrier.
U.S. Pat. No. 4,420,534 discloses the use of a matrix composition consisting of 10-30% of a low molecular weight component chosen from a series of mono- and disaccharides, corn syrup solids, or organic acid with the balance of the mixture being maltodextrin. The matrix is dry blended with an anhydrous liquid flavoring component and melted in a single screw extruder to yield a solid matrix characterized as a glass with a glass transition temperature greater than 40° C.
U.S. Pat. No. 5,972,395 discloses the use of a matrix composed of 15 to 40% of a high molecular weight carrier, preferably a maltodextrin and at least 40% of a low molecular weight carbohydrate, sugar polyol, or adipic acid. The matrix is extruded to yield a solid matrix characterized as a glass.
U.S. Pat. Nos. 5,087,461 and 5,009,900 disclose utilizing a composition consisting of a modified food starch, maltodextrin, polyol, and mono- and disaccharide components. The starch is a chemically-modified water-soluble starch and is used in the amount of 40 to 80% of the total mixture. The balance of the composition is comprised of 10 to 40% maltodextrin, 5 to 20% corn syrup solids or polydextrose, and 5 to 20% mono- or disaccharide. This matrix is said to balance processing response with glass matrix character.
U.S. Pat. No. 5,756,136 discloses the encapsulation of cinnamic aldehyde in a matrix containing at least 25% of a whey protein isolate. The resulting encapsulate exhibits a control release functionality and protection for yeast-leavened dough.
U.S. Pat. Nos. 6,652,895; 6,416,799; 6,187,351; 5,603,971; and 5,987,897 disclose the use of a series of extrusion matrix compositions. The use of water to plasticize the matrix in the extrusion process yields an encapsulated flavor matrix characterized by glass transition temperatures greater than 40° C. In U.S. Pat. No. 6,652,895, a composition containing a carboxylate or sulfate containing food polymer and the presence of calcium ions in the melt is disclosed. In U.S. Pat. No. 6,416,799, a composition containing a maltodextrin with buffering organic acid-acid salts is disclosed. In U.S. Pat. No. 6,187,351, a composition containing 2 to 45% of a food polymer, 25 to 80% of a maltodextrin, and 10 to 30% of a mono- or disaccharide or 24 D.E. to 42 D.E. corn syrup solids is disclosed. The matrix is dry blended, fed into the extruder with the required water plasticizer and flavor, and the resulting encapsulate is obtained as a glassy solid exhibiting a glass transition temperature greater than 40° C. The disclosed polymers include modified celluloses, high methoxy pectin, gum arabic (acacia), locust bean gum, guar gum, and lesser gums such as gum ghatti, gum tragacanth and gum karaya. Also disclosed are proteins such as gelatin and α-casein, microbial gums such as xanthan and gellan, pregelatinized starches in addition to other carbohydrate polymers such as inulins, β-glucans and konjac flour.
U.S. Patent Application US2002/0189493 A1 discloses the use of majority, single polymer component compositions with melt extrusion encapsulation. In one case, a matrix composed of a binary polymer composition selected from the group of gelatin, hydrolyzed gelatin, larch gum and gum arabic at 0 to 50% of the individual polymers is disclosed.
U.S. Patent Application US2002/0187223 A1 teaches the use of prehydrated agar agar (at 1-7% levels) with other carriers which are mixed with a flavor, extruded and dried to form a glassy matrix encapsulating media.
U.S. Pat. No. 4,816,298 discloses the preparation of a cold-water dispersible granular composition comprising a plasticizer and thermally moldable polymer. The polymers are selected from the group of methyl cellulose, hydroxypropyl methylcellulose, carboxymethyl cellulose, and hydroxypropylcellulose and are extruded at an elevated temperature with plastizer to yield a cold-water dispersible matrix.
In a number of the cited patents which disclose melt extrusion, the matrix compositions were carefully defined to accommodate processing limitations of the extruder as well as to generate a stable matrix in the glassy state and characterized by a glass transition temperature of greater than 40° C.
Formation of a matrix in the glassy state is of particular value for encapsulation of water-soluble flavorings and extracts. The role of water as a plasticizing agent conflicts with the desired results, because water has the effect of lowering the glass transition temperature (Tg) of the glassy matrix. In model studies of a number of food carbohydrate systems, the upper limit of water content is approximately 7 to 10 wt. % for lower molecular weight components such as mono- and disaccharides, maltodextrins, food polymers and combinations of these agents. At higher water contents, the Tg is lowered to the extent that the matrix is in the undesirable rubbery, plastic or fluid state at room temperatures.
In order to insure a higher Tg, several options are available. By limiting the class of encapsulate materials to lipophilic materials such as citrus oils, plasticizing moisture can be removed by a boil off process as described in U.S. Pat. Nos. 2,856,291; 2,857,821; 2,809,895; 3,041,018; 3,314,803; 3,704,137; and 4,707,367. Alternatively, the use of melt encapsulation disclosed in U.S. Pat. No. 4,420,534 limits the flavoring agents to materials with lower vapor pressure which can be admixed to the premelt composition. In addition, flavorings which are in the form of aqueous extracts, water, or alcohol-water solutions will result in a product with a Tg much below 25° C. leading to plastic flow and loss of volatiles upon storage.
Similarly, in U.S. Pat. Nos. 5,009,900 and 5,972,395, the flavorings are limited to those with limited volatility, and total moisture level in the product is less than 11% by weight. Many of the key topnotes and unique flavor components of complex flavors have high vapor pressures at room temperature and are not easily encapsulated by such a process.
Matrix improvements for the continuous melt extrusion process are described in U.S. Pat. Nos. 6,652,895; 6,416,797; 6,187,351; 5,603,971; and 5,987,897. The use of modified starch and food polymers with low molecular weight carbohydrate plasticizers is detailed to yield encapsulates in a glassy matrix with a Tg greater than 40° C. However with these matrices the flavor loads are generally limited to 10 wt. % or less.
Preparation of a solid in the glassy state is dependent upon both matrix composition and the process used to generate the encapsulating material. The advantages of retaining the glass form of the matrix include increased physical stability of the solid, reduced loss of incorporated volatiles, and reduction of deleterious intermolecular reactions and oxidation. A detailed discussion of the physical chemistry of water-food polymer interactions relating to the glassy state can be found in H. Levine and L. Slade, “Glass Transitions in Foods,” in Physical Chemistry of Foods, H. Schwartzberg and R. Hartel, Eds., Marciel Dekker, New York, pp. 83-205, 1992; and in H. Levine and L. Slade, “Water as a Plasticizer: physico-chemical aspects of low-moisture polymeric systems,” in Water Science Reviews, vol. 3, F. Franks, Ed. Cambridge University Press, London, pp. 79-185, 1988, which are incorporated herein by reference. The role of water as a plasticizer with food polymers, as well as the relationships between molecular compositions and dynamics of interactions between various components, are discussed in these references.
Thus, there remains a need for encapsulation compositions in which an encapsulate is encapsulated in a matrix which is stable in the glass state at ambient temperatures. In particular, there remains a need for flavor encapsulation compositions in which a flavoring agent is encapsulated in a matrix which is stable in the glassy state at room temperature, i.e., has a Tg sufficiently high to prevent caking and plastic flow at ambient room temperatures. There also remains a need for flavor encapsulation compositions which have a high Tg and are amenable for encapsulating volatile and sensitive flavor components. There also remains a need for encapsulation compositions which exhibit controlled release functionality. Finally there also remains a need for processes for preparing such compositions.